Sediment transport characteristics above a gobi surface in northwestern China, and implications for aeolian environments

Abstract

Gobis (gravel deserts) cover large areas in northwestern China and other parts of the world, but sediment transport above gobi surfaces has not been widely investigated; thus, there is insufficient empirical data to support dust source identification. In the present study, we used the LDDSEG vertically segmented sediment sampler to collect sediment transport data above a gobi surface. The results demonstrated that the sediment transport rate above the gobi surface was larger than that above a sandy surface, with rates as high as 9.7 kg m^-1h⁻¹. The transport flux can be expressed as a Gaussian peak function, with the maximum sediment transport at 0.05 to 0.09 m above the surface. Principal-components analysis (PCA) indicated that the mean grain size of the transported sediment was controlled mainly by the content of silt and clay (<63 μm) and fine sand (125 to 250 μm); this explains the inflection height for sediment transport. PCA also indicated that dry lacustrine deposits were the main sediment source in the study region. About 90% of the cumulative sediment transport occurs at a height below 0.65 m. Our results indicate that sediment transported over a gobi surface has higher trajectories and longer distances than above a sandy surface. The larger silt and clay component (about 30%) of the sediment transported over the gobi surface means that gobi surfaces are important dust sources in northern China, although the dust likely originated from dry lacustrine sites upwind of the study site.